Method—Using Microelectrodes to Explore Solid Polymer Electrolytes

Abstract

Solid polymer electrolytes are an emerging technology in electrochemistry driven by their use in energy applications such as fuel cells, electrolyzers, and solid-state batteries. Compared to traditional liquid electrolytes, solid polymer electrolytes provide safer, cheaper, and potentially improved device performance. However, there is a lack of standard experimental methods for studying solid electrolytes. Microelectrodes have inherent benefits capable of filling this experimental gap due primarily to their integration into model electrochemical cells with solid electrolytes that represent complex interfaces, enabling additional insight into reaction processes. In this tutorial review, we explore the use of microelectrodes to study solid polymer electrolytes, beginning with a brief history of the field including common experimental cell designs and their benefits and drawbacks. Methods of evaluating essential kinetic and mass-transport parameters are then examined. In addition, the key studies of the past 30 years utilizing microelectrode cells and solid polymer electrolytes are summarized, with important results highlighted and compared. Finally, future studies of solid polymer electrolytes with microelectrodes and potential new avenues of research are commented on.

Engineering Catalyst Layers for Next‐Generation Polymer Electrolyte Fuel Cells: A Review of Design, Materials, and Methods

“…A review and best practice article by Petrovick et al. [ 95 ] has recently made efforts to mitigate these issues.…”

Gas Mass-Transport Coefficients in Ionomer Membranes Using a Microelectrode

“…Cyclic voltammetry (CV) ascertained the electrochemical surface area (ECSA) of the microelectrode surface by evaluating the area of the hydrogen underpotential-deposition region . In this method, the peaks appearing in the approximate range of 0–0.4 V on the CV scan represent hydrogen desorption and adsorption depending on whether the current is positive or negative, respectively .…”

“…The diffusivity, Henry’s constant, and permeability of oxygen gas in Nafion membranes are well-studied. − Conversely, hydrogen gas is less well-studied, with a primary focus on permeability in-lieu of individual diffusivity and Henry’s constant. ,− There are several methods of interrogating gas-transport properties, including gas crossover, electrochemical monitoring, and permeation experiments. ,,, The apparatus discussed here is a microelectrode, traditionally defined as an electrode smaller than 100 μm in lateral dimension . The primary advantages of microelectrodes are the well-defined working electrode area and extremely low current draw that allow the ohmic potential drop to remain small even when working with relatively high-resistance electrolytes such as solid-state ionomers . In addition, the apparatus acts as a mimic for the environment found in a PEFC, as the electrode can be exposed to the same electrolyte, potential, humidity, and gases as in a functioning PEFC, but in a much more controlled manner .…”

“…The primary advantages of microelectrodes are the well-defined working electrode area and extremely low current draw that allow the ohmic potential drop to remain small even when working with relatively high-resistance electrolytes such as solid-state ionomers . In addition, the apparatus acts as a mimic for the environment found in a PEFC, as the electrode can be exposed to the same electrolyte, potential, humidity, and gases as in a functioning PEFC, but in a much more controlled manner . This gives microelectrode assemblies a distinct advantage over traditional aqueous electrolyte techniques, such as rotating disk electrodes (RDEs), when studying PEFC electrochemistry …”

“…In addition, the apparatus acts as a mimic for the environment found in a PEFC, as the electrode can be exposed to the same electrolyte, potential, humidity, and gases as in a functioning PEFC, but in a much more controlled manner . This gives microelectrode assemblies a distinct advantage over traditional aqueous electrolyte techniques, such as rotating disk electrodes (RDEs), when studying PEFC electrochemistry …”